1. Field of the Invention
The present invention relates to a process and an apparatus for manufacturing pneumatic tyres.
2. Description of the Related Art
A tyre for vehicle wheels generally comprises a carcass structure including at least one carcass ply having respectively opposite end flaps in engagement with respective annular anchoring structures, integrated into the regions usually identified as “beads” and having an inner diameter substantially corresponding to a so-called “fitting diameter” of the tyre on a respective mounting rim.
Associated with the carcass structure is a belt structure comprising one or more belt layers located in radial superposed relationship with respect to each other and to the carcass ply and having textile or metallic reinforcing cords with a crossed orientation and/or substantially parallel to the circumferential extension direction of the tyre. A tread band is applied at a radially external position to the belt structure, which tread band too is of elastomeric material like other semifinished products constituting the tyre.
In addition, respective sidewalls of elastomeric material are applied at an axially external position, to the side surfaces of the carcass structure, each extending from one of the side edges of the tread band until close to the respective annular anchoring structure to the beads. In tyres of the tubeless type, an airtight coating layer, usually referred to as “liner”, covers the inner tyre surfaces.
Subsequently to building of the green tyre carried out through assembly of respective components, a moulding and vulcanisation treatment is generally carried out, which treatment aims at determining the structural stabilisation of the tyre through cross-linking of the elastomeric compounds, and also at imprinting a desired tread pattern therein, as well as possible distinctive graphic marks at the tyre sidewalls.
The carcass structure and belt structure are generally made separately from each other in respective work stations, to be mutually assembled at a later time.
In more detail, manufacture of the carcass structure first contemplates application of the carcass ply or plies onto a building drum, and subsequently the annular anchoring structures to the beads are fitted or formed on the opposite end flaps of the carcass ply or plies that are then turned up around the annular structures themselves so as to enclose them in a loop and form a so-called “carcass sleeve” which is substantially cylindrical.
Simultaneously, on a second or auxiliary drum a so-called “outer sleeve” is made which comprises the belt layers applied in radially mutually superposed relationship, and possibly the tread band applied at a radially external position to the belt layers. The outer sleeve is then picked up from the auxiliary drum to be coupled to the carcass sleeve. To this aim the outer sleeve is disposed coaxially around the carcass sleeve and afterwards the carcass ply or plies are shaped into a toroidal configuration by axial mutual approaching of the beads and simultaneous admission of fluid under pressure to the inside of the carcass sleeve, so as to determine radial expansion of the carcass plies until causing adhesion of same against the inner surface of the outer sleeve.
Assembling of the carcass sleeve to the outer sleeve can be carried out on the same drum as used for manufacture of the carcass sleeve, in which case reference is made to a “unistage building process” or “unistage process”.
Also known are building processes of the so-called “two-stage” type in which a so-called “first-stage drum” is employed to make the carcass sleeve, while assembly between the carcass structure and outer sleeve is carried out on a so-called “second-stage drum” or “shaping drum” onto which the carcass sleeve picked up from the first-stage drum, and subsequently the outer sleeve picked up from the auxiliary drum, are transferred.
Document EP 0 197 298 A2 discloses a method of manufacturing a tyre for vehicle wheels for accomplishment of which the beads are to be installed in the radially internal circumference of the rim on which the tyre itself is mounted. The carcass is first assembled with the respective beads provided with longitudinal-stress-resistant and compression-resistant cores, onto a drum so as to form a cylindrical green tyre in which the beads radially extend inwardly and the axially internal surfaces of the beads form a right angle with the cylindrical wall of the green tyre. The green-tyre beads are preformed/moulded and prevulcanised so as to give them a finished and steady shape. Therefore, the shape of the beads and of the immediately adjacent regions is not subject to any further modification during the following manufacturing steps. The beads are subsequently rotated through about 180° around the respective resistant cores. After giving the green tyre a toroidal shape, the green tyre is provided with tread band and sidewalls and lastly submitted to full vulcanisation.